1. Field of the Invention
The present invention relates to spark plugs for use in internal combustion engines and, more particularly, to a spark plug having a star-shaped or a multi-point firing cap.
2. Description of the Related Art
The most common type of conventional spark plug has a central electrode spaced at a specified gap from a L-shaped electrode. The L-shaped electrode is electrically connected to an outer metallic shell of the spark plug that contacts the engine, providing an electrical ground for the spark plug. When the spark plug fires, a spark jumps between the central electrode and the L-shaped ground electrode.
Such conventional spark plugs serve their purpose of igniting the air/fuel mixture in an internal combustion engine. However, the present inventor has discovered that there is significant room for increasing combustion efficiency, and thereby also reducing engine emissions, engine operating temperature and damage resulting from combustion within the exhaust system, through the use of improved spark plug technology.
Various conventional spark plug designs have been proposed. However, none has been found to adequately address these problems.
The present invention addresses such problems by providing a spark plug that generally is capable of firing multiple sparks simultaneously. In this regard, while some conventional spark plugs have multiple points that are capable of sparking, the present inventor has discovered that such conventional spark plugs nevertheless only reliably fire from one point at a time. It is believed that slight physical differences cause one of the points to be the path of least resistance and, once that point fires, the ionization of air within the gap corresponding to that point reduces the path resistance even further, precluding the other points from firing. In such conventional spark plugs, when the firing point has become sufficiently fouled, its resistance to firing becomes great enough that one of the other points becomes the path of least resistance and it fires instead. As a result, only one point fires at a time, leading to less than optimal combustion within a cylinder. The present invention addresses this problem in the following manner.
In one aspect, the invention is directed to a spark plug that includes a central electrode having a proximal end and a distal end and a cap having a central portion and plural projections extending radially from the central portion. Thus, in one embodiment the cap is star-shaped and may be bent into a dome shape. The cap has a proximal side and a distal side, and the proximal side of the cap is attached to the distal end of the central electrode. The cap is electrically conductive, having a first electrical conductivity. A central portion of the cap defines a hole and has a thickness in a location of the hole, and the central electrode extends into the hole of the cap but terminates prior to the distal side of the cap. A filler material, which may have been deposited as a fusion medium, is disposed within a portion of the hole that is not occupied by the central electrode, with the filler material having a second electrical conductivity that is lower than the first electrical conductivity.
In a further aspect, the invention is directed to a spark plug that includes a central electrode having a proximal end and a distal end and a cap having a central portion and plural projections extending radially from the central portion. The cap has a proximal side and a distal side and the proximal side of the cap is attached to the distal end of the central electrode. The cap is comprised mostly of a first material having a first electrical conductivity and also of a second material having a second electrical conductivity that is lower than the first electrical conductivity, with the second material being disposed toward the distal side of the cap.
By virtue of the foregoing arrangements, a spark plug according to the present invention often can provide multiple simultaneous sparks, frequently at least one from each radial projection. As a result, more efficient combustion often can occur, yielding improved efficiency and reduced emissions of certain types of pollutants. In addition, more efficient combustion reduces the likelihood of combustion within the exhaust system, thereby reducing damage from such combustion and reducing engine operating temperature.
The present invention also concerns improved spark plug manufacturing. Thus, in a still further aspect, the invention is directed to a method for manufacturing a spark plug. A cap is fabricated, the cap having a central portion and plural projections extending radially from the central portion, with the central portion of the cap defining a hole through the cap and with the hole having a depth. An electrode is inserted into the hole, but only through a portion of the depth of the hole, and the cap and the electrode are heated so that fusion begins to occur. Attachment material is then deposited so as to fill at least a portion of the depth of the hole not occupied by the electrode.
The above method often can efficiently provide a spark plug that is capable of firing from multiple radial projections simultaneously, thereby improving combustion efficiency and providing the associated benefits described above.
The foregoing summary is intended merely to provide a brief description of the general nature of the invention. A more complete understanding of the invention can be obtained by referring to the claims and the following detailed description of the preferred embodiments in connection with the accompanying figures.